Rowdy celebrations of Osama bin Laden’s death gave way to a more sober mood Monday, as Americans reflected on the terrorist leader’s bloody legacy and their government girded for the possibility of retaliatory attacks.

Crowds of revelers at the World Trade Center site dispersed by Monday morning, leaving behind small memorials: candles, signs and flowers, their stems woven through the fence surrounding Ground Zero.

"It’s bittersweet," said James Cahill, chairman of the New Jersey 9/11 Memorial Foundation and a father whose son died at the Twin Towers. "Justice has been served, but it doesn’t do much to ease the pain or the loneliness of losing a loved one."

The White House announced Monday night that President Obama will travel to New York on Thursday to visit Ground Zero and meet with the families of those killed on 9/11.

In Washington, meanwhile, top officials cautioned that the death of bin Laden would not spell an end to combat operations overseas, even as they lauded the success of a risky U.S. attack on the terrorist leader’s high-security compound early Monday in Pakistan.

John Brennan, the president’s top counterterrorism adviser, said killing bin Laden was like "decapitating the head of the snake," but warned his terrorist organization, al Qaeda, "may be a mortally wounded tiger that still has some life left in it."

Bin Laden, who spent nearly a decade in hiding after orchestrating the Sept. 11, 2001, terrorist attacks on the World Trade Center and the Pentagon, was killed in a firefight with U.S. forces Monday.

He was buried at sea, denying a marked final resting place for America’s most wanted and despised fugitive. He was 54.

Before dropping bin Laden’s body in the North Arabian Sea — Islamic tradition requires a speedy burial, and officials doubted they could find a country willing to house his remains — they performed DNA tests confirming his identity, according to the Associated Press.

Obama, speaking during a ceremony for Medal of Honor recipients Monday, said the world is "a better place" without bin Laden.

"Today we are reminded that as a nation, there’s nothing we can’t do when we put our shoulders to the wheel, when we work together," the president said. "And we remember the sense of unity that defines us as Americans."

HIGH ALERT

At the same time, security was beefed up at airports, rail lines and other key transit points as a precaution against retaliatory attacks.

"The world’s most wanted international terrorist is no more, but the death of bin Laden does not represent the demise of al Qaeda affiliates and those inspired by al Qaeda, who have and will continue to engage in terrorist attacks," Interpol Secretary-General Ronald Noble said in a statement.

In addition, the U.S. State Department placed its embassies on alert and issued a worldwide travel alert, saying there was an "enhanced potential for anti-American violence given recent counterterrorism activity in Pakistan."

The Port Authority of New York and New Jersey said it will deploy more police "out of an abundance of caution."

At Newark Liberty International Airport — where one of the hijacked planes took flight almost 10 years ago — lines moved smoothly and it seemed an average day as the "God Bless the USA" by Lee Greenwood played over the terminal’s sound system.

Jatin Shah, 30, of India said he felt better knowing bin Laden was out of the picture.

"The world will be a little safer, for now," he said.

THE OPERATION

The inner details of the long hunt for a man whom U.S. officials hold responsible for thousands of deaths around the world were still emerging. Administration officials described an operation that took years of intelligence gathering that led to a daring 40-minute raid on bin Laden’s compound. After years of fruitless searches, intelligence reports pinpointed bin Laden’s location in a fortress-like compound in Abbottabad, a city near Pakistan’s capital, senior administration officials said. The structure, built in 2005 at an estimated cost of $1 million, was described as having "extraordinary" security measures, including walls up to 18 feet tall and topped with barbed wire.

Elite U.S. forces, ordered into action by Obama, descended by helicopter on bin Laden’s hide-out before dawn. The al Qaeda leader fought back and was killed in a firefight along with one of his sons and two associates, officials said. Bin Laden’s wife was shot in the calf but survived, a U.S. official said.

Bin Laden died from a bullet to the head and his body was taken by U.S. forces.

"Justice has been done," Obama announced at the White House on Sunday night.

No Americans were killed, but one of the helicopters suffered a mechanical failure and was subsequently destroyed by U.S. forces, the officials said.

PAKISTAN

New Jersey Gov. Chris Christie praises President Barack Obama for killing of Osama bin Laden Appearing at a State House press conference with State Sen. Steve Sweeney, New Jersey Gov. Chris Christie answers questions about the death of Osama bin Laden saying he hopes it provides a sense of closure for the families of victims of the Sept. 11, 2001 terrorist attacks. Christie also praises President Barack Obama for ordering the military operation that killed Obama saying the president "deserves extraordinary credit."

The operation raised more questions about whether America’s purported Pakistani allies were turning a blind eye toward terrorist activities. Bin Laden was found not in the lawless tribal region along the border with Afghanistan, but just a half mile away from a military academy for top Pakistani officers, the Associated Press reported.

Sen. Frank Lautenberg (D-N.J.) said the United States should withhold $3 billion in aid for Pakistan until officials there show they are "not shielding terrorists."

Wajid Shamsul Hasan, Pakistan’s high commissioner to the United Kingdom, said the country did not know bin Laden was in Abbottabad.

"Had we known it we would have done it ourselves," Hasan told the BBC. "The Americans knew it and they carried out the operation themselves and they killed Osama bin Laden and then later our president of Pakistan was informed that the operation was successful, and that’s it."

Secretary of State Hillary Clinton said the United States will keep working closely with Pakistan to fight terrorists.

"Continued cooperation will be just as important in the days ahead, because even as we mark this milestone, we should not forget that the battle to stop al Qaeda and its syndicate of terror will not end with the death of bin Laden," she said. Clinton said she hopes bin Laden’s death sends a message to America’s enemies.

"You cannot defeat us," she said. "But you can make the choice to abandon al Qaeda and participate in a peaceful political process."

Although some experts have questioned the continuing importance of bin Laden to al Qaeda’s decentralized terrorist network, the charismatic leader had remained a powerful symbol.

"There’s nobody in the world that can take his place," said former New Jersey Gov. Tom Kean, who led the 9/11 commission. "It will be an al Qaeda without his inspiration."

EXULTANT AMERICANS

On Sunday night, word of bin Laden’s death leaked out shortly before Obama’s announcement, and revelers quickly began streaming toward the White House and Ground Zero. Three friends in Sussex County heard about bin Laden’s death on Facebook last night, and went straight to the train station. They were in Manhattan by about 2 a.m.

"I think we sang the national anthem like four times," said Kevin Van Orden, 19, who was dressed in his older brother’s Army fatigues.

Derek Smith, also 19, said they went to Ground Zero to pay their respects to the victims of the terror attacks.

"It happened when we were in fourth grade, that’s more than half my life," he said. "That day changed everything."

More people gathered in Times Square to celebrate, waving American flags and cheering as news of bin Laden’s death scrolled across the news ticker. Some wrapped American flags around their waists, shoulders, or heads. Others were in pajama pants, looking as if they ran out the door to celebrate the minute they heard the news.

Pravesh Shiwnaraia, 27, and Vinay Roopchan, 21, both of Queens, held a large American flag between them.

"We’re proud to be Americans tonight," Roopchan said. He added, "It’s not all in vain anymore."

By the time the sun rose Monday morning, the scene had shifted. The area was bustling by 6 a.m. as construction workers in sweatshirts, neon vests and hard hats gathered outside the fences with steaming cups of coffee. Commuters soon swarmed the site, disembarking from trains en route to their offices, sometimes pausing to take photos with their phones.

Bill Steyert, 67, said for many years, he was "too depressed" to visit Ground Zero. But a few years ago, he said, he started coming to memorials with a sign he’d made, which features a newspaper clipping listing the names of all the victims. Monday, he added to that sign: a cutout of a triumphant headline declaring bin Laden dead.

Said Steyert, "I have very mixed feelings, because I am still grieving, but I am also celebrating that we finally got some justice."

Later in the day, Maria Arevalo, 65, of Paterson, ventured to the site with flowers and a photograph of her son, Kenneth Lira, 28, who worked as a computer engineer for Genuity, and was on one of the South Tower’s top floors when it was hit.

She went with her son’s father, Jose Lira, 65, and her sister, Tone Arevalo, 54.

"I’m not jumping up and down," Maria Arevalo said. "The death of this man doesn’t mean it will ease my pain. My only comfort is the mastermind will not continue killing innocent people.

"I still don’t understand why he did this," Maria Arevalo said of bin Laden. "I wanted to know from him why he killed those innocent people."